Hybridoma producing antibodies to lawsonia intracellularis

ABSTRACT

The present invention relates to the field of animal health and in particular to  Lawsonia intracellularis . In particular, the invention relates to a method of diagnosing  Lawsonia intracellularis  infection and a diagnostic test kit using  Lawsonia intracellularis -specific antibodies. The invention also relates to the use of the method or test kit for diagnosing  Lawsonia intracellularis  infections.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/854,525, filed Aug. 11, 2010, which is a divisional applicationof U.S. application Ser. No. 12/606,179, filed Oct. 26, 2009, now U.S.Pat. No. 7,799,562, which is a divisional application of U.S.application Ser. No. 11/875,538, filed Oct. 19, 2007, now U.S. Pat. No.7,635,590, which is a divisional application of U.S. application Ser.No. 11/158,800, filed Jun. 22, 2005, now U.S. Pat. No. 7,303,891, whichclaims priority to European Patent Application No. EP 04 104 804, filedJun. 24, 2004 and European Application No. EP 04 027 193, filed Nov. 16,2004, the contents of which are hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates to the field of animal health and inparticular to Lawsonia intracellularis. In particular, the inventionrelates to a method of diagnosing Lawsonia intracellularis infection anda diagnostic test kit using Lawsonia intracellularis-specificantibodies. The invention also relates to the use of the method or testkit for diagnosing Lawsonia intracellularis infections.

B. Background of the Invention

L. intracellularis, the causative agent of porcine proliferativeenteropathy (“PPE”), affects virtually all animals, including humans,rabbits, ferrets, hamsters, fox, horses, and other animals as diverse asostriches and emus. L. intracellularis is a particularly great cause oflosses in swine herds in Europe as well as in the United States.

A consistent feature of PPE is the occurrence of intracytoplasmic,non-membrane bound curved bacilli within enterocytes in affectedportions of intestine. The bacteria associated with PPE have beenreferred to as “Campylobacter-like organisms.” S. McOrist et al., Vet.Pathol., Vol. 26, 260-264 (1989). Subsequently, the causative bacteriahave been identified as a novel taxonomic genus and species,vernacularly referred to as Ileal symbiont (IS) intracellularis. C.Gebhart et al., Int'l. J. of Systemic Bacteriology, Vol. 43, No. 3,533-538 (1993). More recently, these novel bacteria have been given thetaxonomic name Lawsonia (L.) intracellularis. S. McOrist et al., Intl.J. of Systemic Bacteriology, Vol. 45, No. 4, 820-825 (1995). These threenames have been used interchangeably to refer to the same organism asfurther identified and described herein.

L. intracellularis is an obligate, intracellular bacterium which cannotbe cultured by normal bacteriological methods on conventional cell-freemedia and has been thought to require attached epithelial cells forgrowth. S. McOrist et al., Infection and Immunity, Vol. 61, No. 19,4286-4292 (1993) and G. Lawson et al., J. of Clinical Microbiology, Vol.31, No. 5, 1136-1142 (1993) discuss cultivation of L. intracellularisusing IEC-18 rat intestinal epithelial cell monolayers in conventionaltissue culture flasks. In addition, H. Stills, Infection and Immunity,Vol. 59, No. 9, 3227-3236 (1991) discusses using Intestine 407 humanembryonic intestinal cell monolayers and GPC-16 guinea pig colonicadenocarcinoma cell monolayers in conventional tissue culture flasks.

In particular, L. intracellularis can be cultivated be methods known inthe art, preferably, according to U.S. Pat. Nos. 5,714,375 and5,885,823. For example, culture cells may first be inoculated with aninoculum comprising L. intracellularis bacteria so as to infect thecells with the bacteria. Numerous cell lines can be used in practicingthe invention, including, but not limited to, IEC-18 (ATCC 1589)—ratintestinal epithelial cells, HEp-2 (ATCC 23)—human epidermoid carcinomacells, McCoys (ATCC 1696)—mouse (non-specified) cells, BGMK(Biowhittaker #71-176)—buffalo green monkey kidney cells, and swineintestinal epithelium cells. The preferred culture cells are HEp-2,McCoys or IEC-18 cells.

If culture cells are used, prior to being inoculated, the cells may bein the form of a monolayer. To form a monolayer, the cells may be seedinto conventional flasks. Each flask is generally seeded with betweenabout 1×105 cells to about 10×105 cells per 25, 75, 150, 850 cm2 flaskor roller bottle mixed with growth media. The growth media may be anymedia for cell cultivation which includes a nitrogen source, necessarygrowth factors for the chosen culture cells, and a carbon source, suchas glucose or lactose. The preferred media is DMEM fortified with Ham'sF 12 with 1-5% fetal bovine serum, although other commercially availablemedia may be used with good results.

Successful cultivation of L. intracellularis is enhanced by maintainingthe culture cells in a constant state of growth. Therefore, the culturecell monolayer should be at about 20 percent to about 50 percentconfluency at the time of inoculation. Preferably, the cells should beat about 30 percent to about 40 percent confluency at the time ofinoculation, most preferably at about 30 percent confluency.

Alternatively, the cells, prior to being inoculated, may be grown insuspension, as described infra. Preferably, the cells are first grown to100% confluency in the form of a monolayer in an adherent type system,e.g., a roller bottle system, and then transferred to 3-3000 liters andgrown in suspension.

The inoculum may be a culture of L. intracellularis obtained frominfected swine or other animals.

The inoculum can be an intestinal homogenate prepared by scraping themucosa off of the ileum of a swine or other animal infected with PPE.When preparing an intestinal homogenate, ileal sections selected forculture should show severe lesions with gross thickening of the gut. Dueto the fragile nature of the bacteria, samples should preferably bestored at −70° C. as quickly as possible after necropsy. An antibioticto which L. intracellularis is resistant such as Vancomycin,Amphotericin B or members of the aminoglycoside group of antibiotics,including Gentamicin and Neomycin, to name a few, is preferably added tothe inoculum to suppress contaminating bacteria while permitting L.intracellularis growth. Whether the inoculum is a pure culture or anintestinal homogenate, inoculation of the culture cells can be performedby various techniques known in the art, given the teachings herein.

The bacteria and/or inoculated culture cells are then incubated under areduced dissolved O2 concentration. At dissolved oxygen concentrationsgreater than 10% L. intracellularis growth is less than optimal withcessation of growth eventually occurring at oxygen concentrationsoutside this range. Preferably, the bacteria and/or inoculated culturecells are incubated in a dissolved oxygen concentration in the range ofabout 0% to about 10%. More preferably, the bacteria and/or cells areincubated in an oxygen concentration in the range of about 0% to about8%, with an oxygen concentration of about 0% to about 3.0% being mostpreferred.

The proper concentration of carbon dioxide is also important to theproper growth of L. intracellularis. At carbon dioxide concentrationsgreater than 0% and less than 4%, non-optimum growth occurs withcessation of growth eventually occurring at carbon dioxideconcentrations outside this range. Preferably, the carbon dioxideconcentration is in the range from about 6% to about 10%, with a carbondioxide concentration of about 8.8% being most preferred.

In addition, the cells are preferably incubated at a hydrogenconcentration in the range from about 73% to about 96%. Nitrogen may beused in place of some or all of the hydrogen present. Most preferably,the cells are incubated in about 0 to about 8.0% O2, about 8.8% CO2, andabout 83.2% H2.

Inoculated cells may be incubated in a dual gas incubator or other gaschambers which contains the proper hydrogen, oxygen and carbon dioxideconcentrations and which allows the cells to be suspended duringincubation. The chamber should comprise a means for maintaining theinoculated cells in suspension, and a gas monitor and supply source tosupply and maintain the proper gas concentrations. The incubationtemperature should be in the range of from 30° C. to about 45° C. and ismore preferably in the range of from about 36° C. to about 38° C. Mostpreferably, the temperature is about 37° C. The necessary equipment forcultivation and attenuation is readily available to those or ordinaryskill in the art given the teachings herein. One example of equipmentsuitable for carrying out the resent invention is a dual gas incubator,e.g., model 480 (Lab-Line, Melrose Park, Ill.) in conjunction withspinner flasks to maintain the cells in suspension. The presentlypreferred equipment comprises a fermentor, bioreactor, stir plate orrotary shaker containing media and capable of maintaining the culturecells in suspension via sparging gas of the appropriate concentration,or other means of mechanical agitation, and continuously monitoringdissolved O2 levels in the media. New Brunswick, Braun and othercompanies make suitable fermentors and bioreactors for this purpose.

By maintaining the inoculated cells in a suspended state duringincubation, maximum growth of the cells, and hence L. intracellularis,is achieved by increasing each individual cell's exposure to growthmedia and the proper mixture of hydrogen, oxygen and carbon dioxide. Theculture cells can be agitated and maintained in suspension by a varietyof methods known in the art including, for example, culture flasks,roller bottles, membrane cultures, biobags, WAVE™ bioreactor systems,and spinner flasks. The cells may be kept in suspension duringincubation by incubating the cells in a spinner flask inside a dual gasincubator or similar apparatus. The term “spinner flask”, as usedherein, means a flask or other container which employs a paddles,propeller or other means to agitate the culture and keep the cellscontained therein in suspension.

Alternatively, the inoculated cells are incubated until the cells reachconfluency and then the cells are placed in a spinner flask containinggrowth media and incubated in a dual gas incubator while spinning theflask. Preferably, the inoculated cells are scraped or trypsinized andpassaged into the spinner flask. This can be achieved by a variety ofmethods known in the art such as using a cell scraper to detach thecells. Once the cells are introduced into the spinner flask, the paddleof the spinner flask is typically rotated in the range of from about 30to about 60 rpm on a magnetic stir plate in order to maintain theinfected cells in suspension.

A portion of the cultivated L. intracellularis is then passaged to freshculture to increase the production of L. intracellularis bacteria. Theterm “passaging” or variations thereof herein means the process oftransferring a portion of the cultivated L. intracellularis to freshculture cells in order to infect the fresh cells with the bacterium. Theterm “fresh”, as used herein, means cells which have not yet beeninfected by L. intracellularis. Preferably such cells are on the averageno more than approximately one day old.

The passage of L. intracellularis in suspension cultures may beaccomplished by removing a portion of the original culture and adding itto a new flask containing fresh culture cells. If the original culturehas a high number of bacteria/ml, for example, greater than about 104bacteria/ml, it is preferable to add between about 1 to 10% (volume tovolume) of culture from the infected flask to a new flask containingfresh cells. This is preferably done when 50-100% of the cells areinfected. If fewer than 50% of the cells are infected, passaging ispreferably accomplished by splitting the culture 1:2 into a new flaskand scaling-up the volume by adding fresh media. In either case, celllysis and other steps are not required, in direct contrast to thepassage of monolayer cultures, as in the prior art.

After sufficient growth of the culture cells and subsequent infection byL. intracellularis, as determined by indirect fluorescent antibody (IFA)staining, TCID50 or another comparable method, at least a portion of thecultivated L. intracellularis bacteria is then harvested. The harvestingstep may be performed by separating the bacteria from the suspension byvarious techniques known to those of ordinary skill in the art, giventhe teachings herein. Preferably, the L. intracellularis bacteria isharvested by centrifuging the contents of all or a portion of thesuspension to pellet the culture cells, resuspending the resulting cellpellets, and lysing the infected cells. Typically, at least a portion ofthe contents is centrifuged at about 3000×g for about 20 minutes inorder to pellet the cells and bacteria. The pellet may then beresuspended in, for example, a sucrose-phosphate-glutamate (SPG)solution and passed approximately 20 times through a 25 gauge needle inorder to lyse the cells. If further purification is desired, the samplescan be centrifuged at about 145×g for about five minutes to removecellular nuclei and debris. The supernatant may then be centrifuged atabout 3000×g for about twenty minutes and the resulting pelletresuspended in an appropriate diluent, such as SPG with fetal bovineserum (to prepare harvested bacteria suitable for lyophilization,freezing, or use as an inoculant) or growth media (to prepare harvestedbacteria more suitable for passaging to fresh cells).

As previously mentioned, effective growth of L. intracellularis forlarge-scale production is enhanced by keeping the tissue cells activelygrowing. Using suspension cultures greatly facilitates keeping the cellsactively growing and permits continuous culture expansion and scale-up.Using a fermentor and between about 0 to 3% dissolved O2 as explainedabove, enables growth of up to 108 bacteria/ml.

When using McCoys or IEC-18 cells, it is preferable to add gelatin,agarose, collagen, acrylamide or silica beads, such as Cultisphere-Gporous microcarriers (HyClone Laboratories, Logan Utah), along with thegrowth media. However, HEp-2 cells and others do not requiremicrocarriers according to the methods used herein.

For culture maintenance purposes, with HEp-2 cultures, preferably 25% to50% of the culture is removed and replaced with fresh media at weeklyintervals. For cell cultures with microcarriers or beads, preferably 25%to 50% of the culture is removed and replaced with fresh media 1-2 timesweekly. For scale-up purposes, an additional 25% to 50% of media, ormedia with microcarriers, may be added to the culture.

Depending upon the rate at which the culture cells become infected,passage to fresh cells generally occurs between about every 2 to about 7days. Assuming that the culture cells become at least 70% infectedwithin 2 to 7 days, preferably passage occurs between about every 5 to 7days.

Diagnosis of L. intracellularis antigen is carried out today by usingdirect immuno-fluorescence and PCR. Diagnosis of antibodies specific toL. intracellularis is carried out today by using immuno-fluorescence.These methods are laborious and time consuming and are not suitable forlarge scale screenings.

Effective diagnosis of PPE has also been hindered by the time requiredto culture the causative bacteria. As a result of the present invention,development of diagnostic tools promoting rapid and accurate assays forthe presence of L. intracellularis in biological samples taken fromswine and other animals susceptible to PPE is now possible.

Therefore, the technical problem underlying the present invention is toprovide improved methods for diagnosis of L. intracellularis disease.

SUMMARY OF THE INVENTION

The present invention relates to the field of animal health and inparticular to Lawsonia intracellularis. In particular, the inventionrelates to a method of diagnosing Lawsonia intracellularis infection anda diagnostic test kit using Lawsonia intracellularis-specificantibodies. The invention also relates to the use of the method or testkit for diagnosing Lawsonia intracellularis infections.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented herein.

FIG. 1. Results of Blocking ELISA according to the invention.

FIG. 2. Results of 301 field sera compared in IFA and ELISA.

FIG. 3. Results of Ileitis blocking ELISA-cross-sectional screenings in3 farms.

FIG. 4. Results of Ileitis ELISA-22 German farms.

FIG. 5. Correlation of ELISA results with clinical symptoms.

DETAILED DESCRIPTION OF THE INVENTION

The solution to the above technical problem is achieved by thedescription and the embodiments characterized in the claims.

The aim of the present invention is to provide a method of diagnosingpre-clinical or clinical L. intracellularis infection. Furthermore, animmune response to L. intracellularis shall be detected and a tool forL. intracellularis epidemiology is to be provided.

This objective has been achieved according to the present inventionwithin the scope of the specification and claims by means of a method ofdiagnosing pre-clinical or clinical L. intracellularis infection.

The invention relates to the detection of antibodies against L.intracellularis and to the detection of L. intracellularis itself. Suchantibodies include any antibody type known to the skilled person, inparticular immunoglobulins of the subtypes IgA, souble IgA, IgM, IgG(IgG1, IgG2a, IgG2b, IgG3), and also IgD, IgE.

To detect antibodies specific for L. intracellularis, according to theinvention, the method is based on the fact that:

a) a liquid sample is taken from a mammalb) the specific binding of such liquid sample to L. intracellularisantigen is detectedc) the result obtained is compared with a control.

As defined above, L. intracellularis also includes fragments orantigenic derivatives of L. intracellularis, which may be used in amethod as above.

Similarly, according to the invention, to detect L. intracellularis, themethod according to the invention is as follows:

the method is based on the fact thata) a liquid sample is taken from a mammalb) the specific binding of such liquid sample to L. intracellularisantibodies is detectedc) the result obtained is compared with a control.

The liquid sample may include any bodily fluid including saliva, sweat,urine, blood, secretions, excretions or other bodily fluid samples knownto the expert in the field. In a preferred embodiment, the liquid sampleis collected using either a collection container (for urine or otherliquid), a syringe/collection tube (for blood) or some type ofcollection swab (for saliva, sweat etc.) Preferably, if the sample instep a) is blood, serum or plasma is isolated from this blood sample andstep b) is carried out with serum or plasma instead of the liquidsample. Subsequently, step c) is carried out as above.

In a preferred embodiment, the method is an immune test. An immune testuses monoclonal antibodies or polyclonal antisera specific to L.intracellularis. Immune tests according to the invention include themethods of detection known in the art such as the ELISA test(enzyme-linked immuno-sorbent assay) or the so-called sandwich-ELISAtest, dot blots, immunoblots, radioimmuno tests (radioimmunoassay RIA),diffusion-based Ouchterlony test or rocket immunofluorescent assays.Other immune tests are the indirect or direct immunofluorescent antibodytest (“IFA”). Another immune test is the so-called Western blot (alsoknown as Western transfer procedure or Western blotting). The purpose ofWestern blot is to transfer proteins or polypeptides separated bypolyacrylamide gel electrophoresis onto a nitrocellulose filter or othersuitable carrier and at the same time retain the relative positions ofthe proteins or polypeptides obtained from the gel electrophoresis. TheWestern blot is then incubated with an antibody which specifically bindsto the protein or polypeptide under consideration. These methods ofdetection can be used by the average skilled person to perform theinvention described herein. Literary references in which the skilledperson can find the above-mentioned methods and other detection methodsare listed as follows: An Introduction to Radioimmunoassay and RelatedTechniques, Elsevier Science Publishers, Amsterdam, The Netherlands(1986); Bullock et al., Techniques in Immunocytochemistry, AcademicPress, Orlando, Fla. Vol. 1 (1982), Vol. 2 (1983), Vol. 3 (1985);Tijssen, Practice and Theory of Enzyme Immunoassays: LaboratoryTechniques in Biochemistry and Molecular Biology, Elsevier SciencePublishers, Amsterdam, The Netherlands (1985). Solid and fluid proteinchip technologies or microarray technologies using labeled or unlabeledreagents are further immune tests according to the invention. Such testare widely described, for example by Kozak K R, et al., Identificationof biomarkers for ovarian cancer using strong anion-exchangeProteinChips: potential use in diagnosis and prognosis. Proc Natl AcadSci USA. 2003 Oct. 14; 100(21):12343-8 (2003), or by Fulton, R. J., etal., Advanced multiplexed analysis with the FlowMetrix™ system. ClinicalChemistry 43 (9), 1749-1756 (1997).

The invention further relates to a diagnostic test kit for detecting L.intracellularis infection which contains all the elements required tocarry out a method of diagnosing pre-clinical or clinical L.intracellularis infection as described herein.

The invention further relates, in particular, to a diagnostic test kitwhich contains antibodies specific to L. intracellularis.

The invention further relates, in particular, to a diagnostic test kit,characterised in that the antibodies according to the invention arepolyclonal.

A diagnostic test kit is a collection of all the components for a methodof diagnosis according to the invention. Some examples (not anexhaustive list) of other elements for performing a process according tothe invention include containers such as 96-well plates or microtitreplates, test tubes, other suitable containers, surfaces and substrates,membranes such as nitrocellulose filter, washing reagents and buffers. Adiagnostic test kit may also contain reagents which may detect boundantibodies, such as for example labelled secondary antibodies,chromophores, enzymes (e.g. conjugated with antibodies) and thesubstrates thereof or other substances which are capable of bindingantibodies.

The L. intracellularis bacteria as disclosed herein or known in the art,or components derived from such bacteria, can be used as an antigen inan ELISA or other immunoassay, such as an immunofluorescent antibodytest (“IFA”), to detect antibodies to L. intracellularis in the serumand other body fluids of animals suspected of being infected with thebacteria. The presently preferred immunoassay is an IFA as described inthe example below. Alternatively, the bacteria of the instant inventioncan be used in a Western Blot assay.

The preferred Western Blot protocol is as follows:

-   -   1. Run antigen on 12% SDS-PAGE and transfer to nitrocellulose        membrane.    -   2. Place membrane in blocking buffer for 2 hours.    -   3. Remove blocking buffer and rinse with PBS for 1 minute.    -   4. Dilute serum in blocking buffer and add to membrane. Incubate        for 2 hours at room temperature.    -   5. Wash 3 times with wash buffer (5 minutes for each wash).    -   6. Dilute a conjugated anti-L. intracellularis specific        antibody, preferably a monoclonal antibody, in blocking buffer        and add to membrane. Incubate for 1 hour at room temperature.    -   7. Wash 3 times with wash buffer.    -   8. Add substrate for 10 minutes or until strong banding occurs.    -   9. Rinse with PBS.    -   10. Air dry and store in the dark.

The conjugate linked to the antibody could be for example an enzyme,such as a. horse radish peroxidase (HRP) or alkaline phosphatase (AP).Alternatively, a chromophore, or any other detectable substance which iscan be quantified in the presence of a substrate, can be used asconjugate.

The most preferred immune test according to the invention is an ELISA.Most preferably, such ELISA is a sandwich ELISA (=capture ELISA). Suchan ELISA is more specific, as it detects with two antibodies specific totwo different epitopes on the same antigen.

In a sandwich ELISA, unlabelled antibodies are coated to the microtiterplates. The L. intracellularis as antigen is subsequently added. After awashing step, the bound L. intracellularis antigen is detected with asecond, labeled, L. intracellularis-specific antibody reactive to adifferent epitope on L. intracellularis.

An exemplary coating procedure is as follows:

The plates are coated with unlabelled antibody, e.g. in 10% Sucrose/10%Normal Horse Serum in ddH₂O and incubated with Lawsonia intracellularisantigen. The plates are then dried and sealed and stored at 37° C.Alternatively, the antibody coated plates are stored and the antigen isadded when the ELISA is conducted.

A preferred ELISA protocol according to the invention is as follows (useof antibody coated plates):

-   -   1. Add 0.1 ml/well antigen diluted in coating buffer. Incubate        for 18 hours at 4° C.    -   2. Wash 3 times with PBS.    -   3. Add 0.25 ml of blocking buffer to each well of plate.        Incubate 1 to 2 hours at 37° C.    -   4. Wash 3 times with wash buffer.    -   5. Dilute serum in blocking buffer and add 0.1 ml to the first        wells of plate. Make serial 1:2 dilutions across the plate.        Incubate for 1 hour at 37.    -   6. Wash 3 to 5 times with wash buffer.    -   7. Dilute a conjugated anti-L. intracellularis specific        antibody, preferably a monoclonal antibody, in blocking buffer        and add 0.1 ml to wells of plate and incubate for 1 hour at 37°        C.    -   8. Wash 3 to 5 times with wash buffer.    -   9. Add substrate.    -   10. Measure absorbance of light with a spectrophotometer.    -   11. Wells in which antigen was not added are used as blanks.    -   12. Positive and negative control swine serum should also be        used with each test.

A preferred ELISA is carried out as follows:

The plates are coated with unlabelled antibody, e.g. in 10% Sucrose/10%Normal Horse Serum in ddH₂O and incubated with Lawsonia intracellularisantigen. The plates are then dried and sealed and stored at 37° C.

-   -   1. Add 90 μl buffer into all wells.    -   2. Add 10 μl serum into selected wells.    -   3. Incubate plate for 1 hour at 37 C.    -   4. Wash plate 3 times with PBST.    -   5. Add HRP conjugated anti-L. intracellularis specific antibody,        preferably a monoclonal antibody diluted in CDS-C+0.5M NaCl, 100        μl/well.    -   6. Incubate plate for 1 hour at 37 C.    -   7. Wash plate 3 times with PBST.    -   8. Add substrate, 100 μl/well and incubate at room temperature        for 10 minutes.    -   9. Add 50 μl stop/well.    -   10. Read the plate at 450 nm in a spectrophotometer.

The most preferred sandwich ELISA protocol according to the invention isas follows:

-   -   1. Add 0.1 ml/well mAb diluted in coating buffer. Incubate for        18 hours at 4° C.    -   2. Wash 3 times with PBS.    -   3. Add 0.1 ml/well antigen diluted in buffer to each well of        plate. Incubate 1 to 2 hours at 37° C.    -   4. Wash 3 times with wash buffer and/or directly add 0.25 ml of        blocking buffer to each well of plate. Incubate 1 to 2 hours at        37° C.    -   5. Wash 3 times with wash buffer.    -   6. Dilute serum in blocking buffer and add 0.1 ml to the first        wells of plate. Make serial 1:2 dilutions across the plate.        Incubate for 1 hour at 37.    -   7. Wash 3 to 5 times with wash buffer.    -   8. Dilute conjugated anti-L. intracellularis specific antibody,        preferably a monoclonal antibody in blocking buffer and add 0.1        ml to wells of plate and incubate for 1 hour at 37° C.    -   9. Wash 3 to 5 times with wash buffer.    -   10. Add substrate.    -   11. Measure absorbance of light with a spectrophotometer.    -   12. Wells in which antigen was not added are used as blanks.    -   13. Positive and negative control swine serum should also be        used with each test.

Antigen as used herein is L. intracellularis as defined above. mAbrelates to a monoclonal antibody specific for L. intracellularis.Preferably, such antibody is an antibody as disclosed below.

Surprisingly, outstanding antibodies were generated to be used in theELISA according to the invention. The antibodies have the followingreference numbers: 301:39, 287:6, 268:29, 110:9, 113:2 and 268:18. Allantibodies are specific for antigens of L. intracellularis bacteria.Preferably as capture antibodies in a sandwich ELISA are 110:9, 113:2 or287:6, and as conjugated antibodies 268:18, 268:29 or 287:6. Mostpreferred as capture antibody is antibody 110:9 and as conjugatedantibody is antibody 268:29.

The antibodies according to the invention are produced by hybridomacells. Said hybridoma cells according to the invention were deposited byDr. M. Merza, in the name of Boehringer Ingelheim Vetmedica GmbH,Ingelheim am Rhein, 55216, Germany, at the Centre for AppliedMicrobiology and Research (CAMR) and European Collection of CellCultures (ECACC), Salisbury, Wiltshire SP4 OJG, UK, as patent depositaccording to the Budapest Treaty. The date of deposit was Sep. 22, 2004.HYBRIDOMA CELL LINE 110:9 is successfully deposited under ECACC Acc. No.04092204. HYBRIDOMA CELL LINE 113:2 is successfully deposited underECACC Acc. No. 04092201. HYBRIDOMA CELL LINE 268:18 is successfullydeposited under ECACC Acc. No. 04092202. HYBRIDOMA CELL LINE 268:29 issuccessfully deposited under ECACC Acc. No. 04092206. HYBRIDOMA CELLLINE 287:6 is successfully deposited under ECACC Acc. No. 04092203.HYBRIDOMA CELL LINE 301:39 is successfully deposited under ECACC Acc.No. 04092205. All the above deposits were tested and confirmed to beviable and capable of reproduction on Sep. 22, 2004. The deposition willirrevocably remove all restrictions on the availability of the depositedmaterial to the public upon the granting of patent based on the presentapplication.

The present invention is further described in the following exampleswhich are provided for illustrative purposes only and are not to beconstrued as limiting. Indeed, other variants of the invention will bereadily apparent to one of ordinary skill in the art.

All publications and patents cited herein are incorporated by referencein their entireties.

A. DEFINITIONS

Before the embodiments of the present invention it must be noted that asused herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural reference unless the context clearly dictatesotherwise. Thus, for example, reference to “a bacterium” includes aplurality of such bacteria, reference to the “cell” is a reference toone or more cells and equivalents thereof known to those skilled in theart, and so forth. Unless defined otherwise, all technical andscientific terms used herein have the same meanings as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. Although any methods and materials similar or equivalent tothose described herein can be used in the practice or testing of thepresent invention, the preferred methods, devices, and materials are nowdescribed. All publications mentioned herein are incorporated herein byreference for the purpose of describing and disclosing the cell lines,vectors, and methodologies as reported in the publications which mightbe used in connection with the invention. Nothing herein is to beconstrued as an admission that the invention is not entitled to antedatesuch disclosure by virtue of prior invention.

As used herein, the term “L. intracellularis” means the intracellular,curved gram-negative bacteria described in detail by C. Gebhart et al.,Intl. J. of Systemic Bacteriology, Vol. 43, No. 3, 533-538 (1993) and S.McOrist et al., Int'l. J. of Systemic Bacteriology, Vol. 45, No. 4,820-825 (1995), each of which is incorporated herein by reference intheir entireties; the causative bacteria which can be obtained from PPEinfected swine or other animals throughout the world given the knowledgein the art and the teachings herein; and variants or mutants of any ofthe above bacteria, whether spontaneously or artificially obtained andDNA, RNA and bacterial proteins specific for L. intracellularis,including proteins expressed in vectors or after in vivo application,and also fragments or antigenic derivatives of L. intracellularis. Thisterm also includes adapted isolates and attenuated isolates as definedbelow.

As used herein, the term ‘adapted isolate’ means any L. intracellularisisolate that is prepared according to the cultivation and passagingtechniques in cell culture or any other technique to replicate L.intracellularis for purposes of antigen preparation.

As used herein, the term “attenuated isolate” means any L.intracellularis isolate that is prepared according to the cultivationand passaging techniques taught herein to achieve avirulence whilemaintaining immunogenic properties when administered to a host animal.

As used herein, the term “large-scale cultivation” means a level ofcultivation of L. intracellularis greater than approximately 2.0 to 3.0liters and includes production on a scale of 100 liters or more.“Cultivation” as used herein, means the process of promoting the growth,reproduction and/or proliferation of L. intracellularis.

EXAMPLES Example 1 1.0 Material

-   anti-Lawsonia hybridomal celline: 372:13, 113:2, 268:18, 287:6,    110:9, 268:29, 301:39.-   Equipment and media for hybridomal cell cultivation.-   Equipment and buffers for purification and HRP conjugation of    monoclonal antibodies (mAb).-   Equipment and solutions for ELISA-   Lawsonia antigen SF 1289 N343 12/20/00-   Lawsonia positive sera: lot#052902pig#26 (experimentally infected),    lot#052902pig#69 (vaccinate)-   Lawsonia negative sera: p 25.8#273 Day 52 6-30-95, 116705

1.1 Methods

The preparation of the monoclonal antibodies was performed according tostandard operating procedures at Svanova Biotech.

1.1.1 Culturing of Hybridomal Cells and Preparation of HRP ConjugatedMonoclonal Antibodies

-   -   To secure the hybridomal cell-lines 15 vials of each cell line        was prepared and stored in −135° C.    -   One vial of each hybridomal cell-line was thawed and the cells        were grown in cell-culture flasks.    -   500 ml to 1000 ml of supernatant from each cell line was        purified and conjugated to horse-radish peroxidase.

1.1.2 Blocking ELISA

The purified and HRP conjugated mAb's were tested for their ability tobe blocked by positive Lawsonia pig sera in ELISA.

-   -   The ELISA plate was coated with Lawsonia antigen in a dilution        of 1/200, 1000/well    -   The pig sera was diluted 1/10, 1000/well    -   The HRP conjugated mAb's were diluted and added, 100 μl/well.        The results are expressed as Percent inhibition (PI) according        to the following formulae:

PI=1−(OD sample/OD mAb)×100.

1.2 Results

1.2.1 Culturing of hybridoma cells and preparation of HRP conjugatedmonoclonal antibodies

-   -   All but one of the mAb's were successfully purified and HRP        conjugated. They had good production capacity.    -   mAb 372:13 had poor production capacity. This mAb was not        successfully HRP conjugated and was therefore not tested in the        blocking ELISA.

1.2.2 Blocking ELISA

-   -   Two positive (#26, #69) and two negative (25.8#273, 116705) sera        were used in the experiments.    -   The experimentally infected sera (#26) inhibited all the six HRP        conjugated mAb's, but in different levels. The sera from a        vaccinated pig inhibited the mAb's to a much lesser extent.    -   The negative sera showed no or very low inhibition.

The results are presented in the table below and in FIG. 1.

mAb Serum 301:39 110:9 268:29 287:6 113:2 268:18 #26 exp 57 45 78 74 4272 + #69vacc 18 23 52 43 45 25 + 25.8#273 7 3 27 20 14 21 − 116705 −7 −9−24 −13 18 −19 −

1.3 Discussion

The results of this study clearly show that one or more of themonoclonal antibodies tested are suited for a blocking ELISA testagainst Lawsonia intracellularis. MAb 268:29, 287:6 and 268:18 show theclearest distinction between the positive and negative sera i.e. arestrong candidates in the development of the blocking ELISA.

Example 2 2.0 Summary

Development and Establishment of a Sandwich b-ELISA Prototype for theDetection of Antibodies to Lawsonia intracellularis:After calculation of sensitivity and specificity by usingimmunoflourescence test IFA as gold standard the following can beconcluded:

-   -   Capture mAb 110:9 gives a clear distinction between positive and        negative samples.    -   Detection mAb 268:29 HRP gives a clear distinction between        positive and negative sera showing a sensitivity and specificity        of 100%.    -   It is recommended that the prototype will be as follows:    -   mAb 110:9 as capture mAb, coated in Nunc maxi-sorp strips C-8    -   Antigen(Ag): Lawsonia intracellularis culture (preferably the        concentrated material produced in R&D at BI)    -   Serum samples diluted 1/10 in 0.5M NaCl/PBST. Incubation for 1        hour at 37 C.    -   HRP conjugated mAb 268:29, lyophilized in CDS-C buffer        containing 0.5M NaCl. Incubation for 1 hour at 37 C.    -   Substrate K-Blue Max, incubation for 10 minutes at room        temperature.    -   Svanova's stop solution

2.1 Material and Methods

The ELISA was performed according to the following procedure:

2.1.0 ELISA Procedure

-   -   Add 900 buffer into all wells.    -   Add 10 μl serum into selected wells.    -   Incubate plate for 1 hour at 37 C.    -   Wash plate 3 times with PBST    -   Add HRP conjugate mAb diluted in CDS-C+0.5M NaCl, 100 μl/well.    -   Incubate plate for 1 hour at 37 C.    -   Wash plate 3 times with PBST.    -   Add substrate, 1000/well and incubate at room temperature for 10        minutes.    -   Add 50 μl stop/well    -   Read the plate at 450 nm in a spectrophotometer.        The results were presented as 1-OD values or 2-PI (percent        inhibition) values i.e. 100-sample OD/mAb OD×100.

2.1.1 Test 1 (ELISA 030922, 030923×2)

C-8 maxi strips coated with mAb 110:9, 113:2, 301:39, 287:6, 268:29, 300ng/wellBlocking of strips with 10% 2251HAS (normal horse serum), 10%sucrose/UHP H₂O.150 μl/well, incubated for 30 seconds at room temperature.Ag # 030619 diluted 1/10 in PBST, 1000/well, 3 hours incubation in 4 C.Strips dried in 37 C for 3 hours. Kept in 4 C.

Sera: IFA pos: #26, #69. IFA neg: #6, C1, D1, E1. Diluted 1/10 in 0.5MNaCl/PBST

Conjugate: 268:18, 113:2, 301:39110:9, 287:6, 268:29 HRP diluted in 0.5MNaCl/PBST.All capture mAb's were tested against all HRP conjugated mAb exceptagainst its own.

2.1.2 Test 2 (ELISA 030924)

Strips coated with 110:9, 113:2 and 287:6 according to test 1 above.

Sera: IFA pos: #26, #69. IFA neg: #6, C1, D1, E1. Diluted 1/10 in 0.5MNaCl/PBST

HRP Conjugatea mAb 268:18, 268:29, 287:6 diluted in 0.5M NaCl/CDS-C(standard buffer for lyophilizing of conjugates as Svanova inproduction).

2.1.3 Test 3 (ELISA 030925)

Strips coated with 110:9, 113:2 and 287:6 according to test 1 above.Sera: 24 sera (10 IFA pos, 10 IFA neg and 4 doubtful) were tested.Dilution: 1/10 in 0.5M NaCl/PBST.Conjugate: 268:18 HRP diluted in 0.5M NaCl/CDS-C

2.1.4 Test 4 (ELISA 030930, 031002, 031008)

Strips coated with 110:9 according to test 1 above.Sera: 21 IFA positive and 69 IFA negative. Dilution: 1/10 in 0.5MNaCl/PBSTConjugate: 268:18 conjugated with HRP and 268:29 conjugated with HRPdiluted in 0.5M NaCl/CDS-C.

2.2 Results

2.2.1 Test 1 (ELISA 030922, 030923×2)

Capture mAb 110:9, 113:2 and 287:6 with conjugates 268:18 and 268:29 and287:6 seems to be the best candidates for the sandwich b-ELISA as thesecombinations showed the best blocking capacity on the positive sera.Sera no #6 scored positive in most of the tests. This was suspected asthis sera also scored positive in the previously developed b-ELISAprototype.

2.2.2 Test 2 (ELISA 030924)

This test was mainly performed to assure that the standard buffer usedto lyophilizing of the conjugate could be used. The results show thatblocking was achieved with the positive sera. The best blocking wasfound with detection mAb 268:18 or 268:29.

2.2.3 Test 3 (ELISA 030925)

The capture mAb 110:9 was found to be the best choice as it gave theclearest differentiation between positive and negative samples.

2.2.4 Test 4 (ELISA 030930, 031002. 031008)

Obtained OD and PI values can be found in appendix 5. When plotting theOD values against the IFA results HRP conjugated mAb 268:29 gives theclearest distinction between positive and negative samples with a 100%sensitivity and specificity. mAb 268:18 also gives a sensitivity andspecificity of 100% but the area between positive and negative samplesis slight. When plotting the PI values mAb 268:18 gives a sensitivity of95.7 and specificity of 100% at cut-off 20.9 while mAb 268:29 gives botha sensitivity and specificity of 100% at cut-off 28.6

2.3. Discussion

After calculation of sensitivity and specificity against theimmunofluorescence test IFA the following can be concluded:

-   -   Capture mAb 110:9 is the best choice as it gives a clear        distinction between positive and negative samples.    -   Detection mAb 268:29 conjugated with HRP is the best choice as        it gives a clear distinction between positive and negative sera        with a sensitivity and specificity of 100%.        It is recommended that the prototype will be as follows:    -   mAb 110:9 as capture mAb, coated in Nunc maxi-sorp strips C-8    -   Ag: Lawsonia intracellularis culture (preferably the        concentrated material produced in R&D at BI)    -   Serum samples diluted 1/10 in 0.5M NaCl/PBST. Incubation for 1        hour at 37 C.    -   HRP conjugated mAb 268:29, lyophlized in CDS-C buffer containing        0.5M NaCl. Incubation for 1 hour at 37 C.    -   Substrate K-Blue Max, incubation for 10 minutes at room        temperature.    -   Svanova's stop solution

Example 3 3.1 Summary

The performed accelerated stability studies indicate that the Lawsoniaintracellularis antigen captured ELISA plate has a stability of at leastone year and that the a-Lawsonia HRP conjugate 268:29 has a stability of6 to 12 months in a lyophilized form.

3.2 Introduction

In order to estimate the stability of the components of a futureLawsonia intracellularis ELISA kit accelerated stability tests has to beperformed. The component to be tested is stored at 37 C for 4 weeks andis thereafter tested in the ELISA in comparison with a component kept at4 C. 4 weeks stability in 37 C indicates a shelf-life of about 12months. This report describes accelerated stability studies performed onthe antigen captured ELISA plate and on the HRP conjugate.

3.3 Materials and methods Accelerated Stability on Plates (ELISA 031024)

Plates were coated with Lawsonia mAb 110:9 blocked with 10% Sucrose/10%Normal Horse serum in ddH₂O and incubated with Lawsonia antigen. Plateswere dried and sealed and put in +37° C. Plates were taken from +37 Cweeks 1, 2, 3 and 4 and stored in a refrigerator. Plates were alsostored in +4 C for the whole test-period as a reference.Positive sera #26, #69 and #06 and negative C2, D1 and E2 were used tocheck the performance of the sandwich ELISA.HRP conjugated mAb 268:29 lot #030120 was used.

Accelerated Stability on Lyophilized Conjugate (ELISA 031027)

HRP conjugated mAb 268:29 lot #030120 was diluted 1/1000 in CDS-C bufferdispensed into glass bottles and lyophilized according to standardprocedures. Four lyophilized bottles were stored at +37 C for 1, 2, 3and 4 weeks. Bottles were also stored at 4 C. The different bottles weretested in the sandwich ELISA.As positive serum #26 was used and negative serum 030926 were used.It was found that a dilution of 1/1000 of the conjugated antibody(“conjugate dilution”) gave too high OD values in the test. Theconjugated antibody was therefore titrated in the plate to obtain acorrect signal for the test.

3.4. Results Accelerated Stability on Plates

A big drop in OD values were seen after week 1 compared to the OD valuefrom the strips kept in +4° C. No big differences were seen whencomparing week 1 to 4.When looking at the PI values no significant was found between week 1through 4 and +4° C.Accelerated stability on lyophilized conjugateAt a “conjugate dilution” of 1/8000 serum # 26 showed a decrease from0.547 to 0.398 after 4 weeks and serum 030926 dropped from 1,654 to 0.99after the 4 week period.

3.5. Discussion

The performed accelerated stability studies indicate that the Lawsoniaintracellularis ELISA plate has a stability of at least one year. Theanti-Lawsonia HRP conjugated 268:29 antibody showed a 40% decrease in ODvalue against the negative sera and after 4 weeks. This might indicatesome instability of the conjugate. When calculating on the OD values a40% decrease of a signal at 1.5 means and OD value of 0.9 after 1 yearwhich is still within the acceptance criteria.

Example 4 4.1. Summary

The verification of the prototype (plate batch 040107) was performed bytesting 50 sera previously used when developing the prototype. Theverification study showed a 100% agreement with the positive sera while2 of the 25 negative sera scored positive in the verified batch.It was found that normal horse serum can be used in the CDS-C bufferinstead of swine sera which is the case today.It was found that PBST containing 0.042% PVP showed similar results asusing the PBST tablets (that contains PVP).

4.2. Introduction

In order to verify the sandwich ELISA prototype a larger number of serahave to be tested on a large scale produced plate batch. The study wasperformed on plate batch 040107 that was tested by examining 50 serumsamples that had previously been used to develop the prototype.Buffer CDS-C is used as preservative when lyophilizing the HRPconjugate. This buffer contains swine sera. As it can be problematic inthe future to find Lawsonia negative sera to be used in the CDS-C bufferan alternative has to be tested. In this study normal horse serum andfoetal bovine serum were tested.

The majority of the laboratory work on this ELISA has been performedwith PBST tablets. It has been seen that the 20× conc. PBST that isincluded in Svanovir kits can not be used since the test will then notcorrectly differentiate between positive and negative samples. Whencomparing the recipes of the tablets and the 20× conc. PBST it was foundthat all components were the same except for 0.042% PVP(Polyvinylpyrrolidone K25) that was included in the tablets as astabilizing factor. Experiments showed that when adding the PVP to the20×PBST the same results as the tablets will be achieved.

4.3. Materials and Methods Verification of Prototype (ELISA 040312)

50 sera (received from Bioscreen) previously tested in the prototypeELISA was tested on the large scale plate batch # 040107. PBST 20× concbuffer with 0.042% PVP was used. Lyophilized conjugate batch 040308 wasused.CDS-C Buffer with Normal Horse Serum

Test ELISA 040203

CDS-C buffer was prepared with; 1—swine serum (as in TJ4/05F), 2—withnormal horse serum and 3—with foetal bovine serum. The buffers weretested as conjugate buffer in the ELISA.Serum tested were gris 2, 4, 13 and 17, 1-29664, 3-29664, A-27239,B-27239, #26 and C2. HRP conjugated mAb 268:29 lot #030318 was used. 20×conc PBST with 0.042% PVP was used

Test ELISA 040311

CDS-C buffer containing normal horse serum has been used to preparelyophilized conjugate at two occasions (040211, 040308). The conjugatewas prepared to obtain a final dilution of 1/20k, 1/25k and 1/30k.Freshly prepared conjugate was tested in parallel. Serum #26, 1-29664,3-29664, A-27239, B-27239, pos pool 030926 and neg pool 030926 wereused. HRP conjugated mAb 268:29 lot #030318 was used. 20× conc PBST with0.042% PVP was used.PBST with PVP (ELISA 040301)PBST buffer 20× concentrated was diluted 1/20 and a final concentrationof 0.042% PVP was added. This buffer was tested in parallel with PBSTtablets (already containing PVP) and 20× conc PBST buffer diluted 1/20.The buffers were used in all steps, i.e. in the sample and conjugatedilution buffer as well as in the washing buffer.Serum #26, E1, 1-29664, 3-29664, A-27239, B-27239 and gris 13 were used.HRP conjugated mAb 268:29 lot #030318 was used. As conjugate bufferCDS-C with swine serum was used.

4.4. Results Verification of Prototype

The results show that all 25 previously positive sera also scoredpositive in the verification batch.Two out of the 25 previously negative sera scored positive.CDS-C Buffer with Normal Horse SerumThe buffer containing normal horse serum showed similar results as theone with swine sera.The reading of the lyophilized HRP conjugated mAb decreased at the most0.4 OD when compared to the freshly prepared conjugate. This drop wasnoticed in both batches of lyophilized conjugate. It is not affectingthe test performance as the calculated PI values corresponded wellregardless of obtained OD values.PBST with PVPThe results show that 20× concentrated PBST solution diluted 1/20 withaddition of 0.042% PVP gave similar results as the PBST tablets while20× conc PBST diluted 1/20 without the PVP showed false negativeresults.

4.5. Discussion

The verification of the prototype (plate batch 040107) was performed bytesting 50 sera previously used when developing the prototype. Theverification study showed a 100% agreement with the positive sera while2 of the 25 negative sera scored positive in the verified batch. The“false” negative results are acceptable as the major importance of thistest is to detect positive samples. It has also not been proven that theresults from the previous testing are indeed true.

It was found that PBST containing 0.042% PVP showed similar results asusing the PBST tablets (that contains PVP). The future kits willtherefore contain this buffer. A stability study of the PBST 20× concwith PVP has to be performed to ensure the validity of the kits.

Example 5 5.1 Introduction and Objectives

Detection of serum antibodies against Lawsonia intracellularis so far isdone by the use of IFA tests (1). These tests rely on an individual andhighly subjective judgment in interpretation of results. Recently asandwich blocking ELISA was developed using highly specific monoclonalantibodies against L. intracellularis. The data from this test can bemeasured and evaluated on an objective basis, which improvesreproducibility, repeatability and comparative analyses. In this studyfirst comparative data to the IFA test are presented, demonstrating thesuitability and performance of the new test.

5.2 Material and Methods

L. intracellularis antigen grown on a McCoy cell culture and captured bya specific monoclonal antibody on microtiter plates was used to detectantibodies against L. intracellularis in porcine serum samples. Serawere tested in a 1 to 10 dilution. After 1 h of incubation at 37° C.plates were washed with PBS Tween solution, horseradish-peroxidaselabeled monoclonal antibody (different to the capture antibody) wasadded. The plates were incubated for an additional hour at 37° C.Unbound antibodies were removed by washing. After incubation with TMBsubstrate for 10 min at room temperature the reaction was stopped byadding a stop solution. The OD₄₅₀ was read in a photometer for eachwell. Results were calculated as percent inhibition of controls withoutserum.301 field sera, tested in a validated IFA test (2) for antibodiesagainst L. intracellularis, were used to evaluate the new ELISA. Inaddition cross-sectional samples (10 samples each from 9 age groups)from two farms with known Ileitis and one farm with suspected Ileitiswere used to demonstrate the diagnostic value of the ELISA in comparisonto the IFA.

5.3 Results

Many negative sera resulted in negative inhibition values. Therefore thelowest measured value was set to 0 and all other values were related tothis. These data are declared as “relative ELISA values”.Results from the 301 field sera are summarized in FIG. 2. The ELISAclearly discriminates between negative (mean relative ELISA value 36)and positive sera (mean relative ELISA value 89). Majority of thesamples that scored doubtful in the IFA were positive in the ELISA.Results from the cross-sectional screenings in the 3 farms are shown inFIG. 3. Both tests clearly detect antibodies against L. intracellularisin the 3 farms.

5.4 Discussion

In comparison to the IFA test results the ELISA provides a highersensitivity. In some groups of the 3 tested farms the result from theELISA is much more unambiguous than in the IFA test, that gave a lot ofquestionable results, due to unspecific fluorescence. The serologicalprofiles in the 3 herds corresponded well to previously published datafrom European herds (3,4). The increase of ELISA values between thegroup of 10 and 16 weeks old pigs in comparison to the IFA test resultsindicate, that sera with relative ELISA values greater 55 can be judgedas positive.This new test could help to improve diagnosis of Ileitis in routinesamples. The new blocking Ileitis ELISA provides a tool for fast andsensitive screening of large amounts of samples on an objective basis.All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe method described herein without departing from the concept, spiritand scope of the invention. More specifically, it will be apparent thatcertain agents which are both chemically and physiologically related maybe substituted for the agents described herein while the same or similarresults would be achieved. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by thefollowing claims.

Example 6 6.1 Introduction and Objectives

Specific diagnosis of Ileitis so far is done by the use of IFA tests forantibody detection (1,2) or PCR (3,4), histological and immuno-stainingmethods (2, 5, 6) for antigen detection in feces or intestinal tissuesamples. All these methods have specific disadvantages concerningspecificity, contamination risk or workload and are not suitable forroutine herd screenings on a large scale. So most diagnostic tests aredone only for few pigs from a herd. By the use of a recently developedblocking ELISA serological testing becomes easier, more reliable andsuitable for herd profiling. Cross-sectional screenings of 22 farms inGermany were performed to demonstrate the diagnostic performance of thenew test.

6.2 Material and Methods

Cross-sectional samples from twenty-two German farms were tested in theELISA. From gilts, sows and pigs 4, 7, 10, 13, 16, 20 and 24 weeks ofage samples were taken on each farm (10 samples in each age group). TheELISA was done as described in example 5.

6.3 Results

In FIG. 4 the mean relative ELISA values from all 22 farms aresummarized. Sera from gilts and sows are highly reactive in the ELISA,whereas results from flatdeck piglets of 4 to 10 weeks of age are low.In the fatteners ELISA values increase from 13 to 24 weeks.In FIG. 5 mean relative ELISA values are correlated with the clinicalsymptoms in the farms. The farms No. 5, 6 and 15 had no clinical entericproblems at the time of sampling. In farm No. 3 piglets from 4 to 13weeks had enteric problems, that were diagnosed as E. coli diarrhea. Infarm No. 18 prior serological tests indicated the presence of Lawsoniaintracellularis in the farm without clinical symptoms. In the farms No.1, 2, 7, 8, 9, 10, 11, 12, 19, 21 and 22 Ileitis was diagnosed beforesampling for this study. The farms No. 4, 13, 14, 16 and 20 reportenteric problems in growers and fatteners, farms No. 4 and 13 withclinical suspected Ileitis. In farm No. 17 no clinical signs of diarrheaare observed, but antibiotics are used in growers and at the beginningof fattening.

6.4 Discussion

The summarized seroprofile from the 22 farms shows high reactivity insows and gilts and rising antibody reaction starting at 13 weeks up to24 weeks. These findings are in agreement with serological datapublished so far for Ileitis (7, 8, 9).Pigs from the farms without diarrhea (No. 5, 6, 15 and 18) and the farmwith E. coli diarrhea (No. 3) showed no significant seroconversion inthe ELISA. In the farms with known Ileitis (No. 1, 2, 7, 8, 9, 10, 11,12, 19, 21 and 22) a clear seroconversion can be detected between week 7and 13.Interestingly the samples from most of the sow and gilt groups arehighly reactive in the ELISA, although most of these pigs have noapparent enteric problems. This might be due to a subclinical infectionwith Lawsonia intracellularis. Results from farm No. 17 seem to indicatea subclinical Ileitis.The new ELISA according to the invention provides a powerful tool forserological diagnosis of Ileitis suitable for routine testing of largesample sizes and cross-sectional herd screenings.

REFERENCES

The following references, to the extent that they provide exemplaryprocedural or other details supplementary to those set forth herein, arespecifically incorporated herein by reference.

-   1. Guedes R M C et al., 2002. Can J Vet Res 66:99-107.-   2. Knittel J P et al., 1998. AJVR 59:722-726.-   3. Biksi I et al., 2002. Proc. 17^(th) IPVS, Ames, Iowa, USA-   4. van Aken N et al., 2002. Proc. 17^(th) IPVS, Ames, Iowa, USA.-   5. Knittel J P et al., 1998. AJVR 59:722-726.-   6. Guedes R M C et al., 2002. Can J Vet Res 66:99-107.-   7. Jones G F et al., 1993. J Clin Microbiol 31: 2611-2615.-   8. Suh-D K et al., 2000. J Vet Sci 1:33-37.-   9. McOrist S et al., 1989. Vet Pathol 26: 260-264.-   10. Huerta B et al., 2003. J Comp Path 129: 179-185.-   11. Biksi I et al., 2002. Proc. 17^(th) IPVS, Ames, Iowa, USA-   12. van Aken N et al., 2002. Proc. 17^(th) IPVS, Ames, Iowa, USA-   13. Holyoake P K et al., 1994. J Clin Microbiol 32: 1980-1985.

1. A diagnostic kit for diagnosis of Lawsonia intracellularis infectioncomprising monoclonal antibody 268:18, secreted by the hybridoma cellline 268:18 deposited at the European Collection and Cell Cultures(ECACC) under the Accession No.
 04092202. 2. The monoclonal antibody268:18 obtainable from the hybridoma cell line 268:18 deposited at theEuropean Collection and Cell Cultures (ECACC) under the Accession No.04092202.